This invention relates to a device for the ignition of a propellant charge, especially for stud driving or setting tools, with a housing wherein a cavity is formed, a piston displaceably guided in the cavity for compressing a gas (air) present in the cavity, and a chamber connected to the cavity by way of an opening, a propellant charge being arranged in this chamber and ignitable by compression of gas upon displacement of the piston.
The ignition of propellant charges can be effected electrically or by mechanical or thermal action. In case of mechanical effect, a firing pin strikes against a case member containing the propellant charge; the primer charge disposed ahead of the propellant charge is heated and ignited in the case member by mutual friction of the particles. One disadvantage of igniting a propellant charge by means of a firing pin resides in the erosive stress and contamination of the barrel by the friction agents contained in the primer charge. Here, adiabatic ignition offers advantages wherein the propellant charge is ignited by a primer charge which, in turn, is initiated by heat produced as a consequence of adiabatic compression of air or gas.
An apparatus for the adiabatic ignition of a propellant charge has been known from DOS 2,103,253. The conventional device comprises a housing wherein a (cylindrical) cavity is formed. A spring-loaded piston is arranged in the cavity for compressing the gas present in the cavity. A barrel for adjoins the cavity in an axial extension of the latter; in the end section of this barrel (cartridge chamber) facing the cavity, a caseless projectile is disposed with a chamber for receiving the propellant charge that is open toward the cavity. The cross-sectional area of the cartridge chamber is relatively large as compared with the cross-sectional are of the cavity. Consequently, the force acting during combustion of the propellant charge on the piston, which piston is in its bottom dead center position, is relatively large. Due to this force, the piston is moved back against the spring so that the gas generation during ignition of the propellant charge is converted only inadequately into a forward motion of the projectile.
U.S. Pat. No. 4,856,433 discloses an initiator for activating an aircraft crew rescue system. A gas-producing charge is ignited in an initiating device. The rescue system is activated by the rising pressure. The gas-generating charge is ignited by adiabatic compression. Also, in this conventional device, the duct leading from the compression chamber to the propellant charge exhibits a relatively large cross-sectional area.